Add riscv test benchmarks

Currently, we're running riscv tests from this test vectors: https://github.com/riscv-software-src/riscv-tests.
There's also benchmark test vectors for the vm https://github.com/riscv-software-src/riscv-tests/tree/master/benchmarks, which are commented out in our tests. https://github.com/ethereum-optimism/asterisc/blob/e1a5b01ae7ffc379681c8c78f148c4d88b42af95/rvgo/test/vm_test.go#L161

In order to run these benchmark tests, we need to fix the elf of asterisc to correctly handle the different Prog.Type in benchmark elf files. https://github.com/ethereum-optimism/asterisc/blob/e1a5b01ae7ffc379681c8c78f148c4d88b42af95/rvgo/fast/elf.go#L40-L50

After fixing the ELF loading, wrap these benchmark tests in go benchmark test suite, so we can actually view the benchmarks.